What is Seasonal Affective Disorder, and How Can I Treat It?

If you’ve been feeling sluggish, overeating, and sleeping in late since the days started getting shorter, it might not just be the post-holiday blues. Feeling depressed and withdrawn during the darker months of the year may be a sign that you suffer from Seasonal Affective Disorder, also known as SAD.

First described in 1984 in a study led by psychiatrist Norman Rosenthal, SAD is a form of clinical depression that generally develops during the fall and winter months, and tapers off in the spring and summer.

“The symptoms of SAD are exactly the same as non-seasonal depression symptoms, which can include a loss of interest or pleasure in normally enjoyed activities, excessive fatigue, difficulty concentrating, a significant change in sleep length, and thoughts about death or suicide,” Kelly Rohan, a professor of psychological science at the University of Vermont who’s done research on treating SAD, told the American Psychological Association. “The only difference with SAD is the seasonal pattern it follows.”

“The main trigger for seasonal affective disorder seems to be shorter days during the fall and winter months.”

The prevalence of SAD in the U.S. can largely depend on geography—the higher in latitude you live, the higher the risk. According to the New York Times in 2007, epidemiological studies estimate that its prevalence can range from 1.4 percent of the adult population in Florida, to 9.7 percent in New Hampshire. As is the case for most types of depression, women are more likely to experience SAD than men—sometimes three to four times more likely. And the disorder seems to be most common for people in their 20s and 30s, dropping off around middle age.

The main trigger for seasonal affective disorder seems to be shorter days during the fall and winter months. Decreased day length, or photoperiod—that is, the time from dawn to dusk—seems to affect the body’s circadian rhythms, which are “physical, mental, and behavioral changes that follow a roughly 24-hour cycle,” according to the National Institutes of Health. Circadian rhythms are regulated by the body’s “biological clock,” which responds to the light and darkness of the surrounding environment.

Melatonin, a hormone produced naturally by the body, gets released at nighttime to control sleep and is on a circadian rhythm. “It rises at night to help us feel sleepy, and it falls in the morning to help us wake up,” Rohan says.

(There is also a more rare form of seasonal affective disorder in which people become depressed in the summer, and become happier in the winter. It’s suspected this has more to do with exposure to too much heat and humidity, rather than shorter day length, says Rohan.)

One popular theory about why some people have SAD is that their biological clocks run notably slower in response to the later dawn in autumn and winter than people without SAD. Their melatonin levels don’t drop fast enough, so when these individuals wake up, their bodies feel like it’s still nighttime. Then they begin to experience depressive symptoms like difficulty waking up in the morning and feeling groggy throughout the day.

How a shift in circadian rhythms can lead to the range of depressive symptoms characteristic of SAD is still not entirely clear, Rohan says. Nevertheless, there are treatment options, which SAD sufferers can tweak and experiment with, depending on the severity of their depression, and under the supervision of a professional.

Light therapy is one possibility, says Rosenthal, a clinical professor of psychiatry at the Georgetown University School of Medicine and author of a book on SAD called Winter Blues. “That can be done informally, like going for a walk on a bright winter day, or bringing more light into a home.”

Your healthcare professional might recommend using a lightbox immediately upon waking, for about half an hour (more or less, depending on the individual). “If you can simulate an early dawn with a big burst of light first thing in the morning, in theory, you’re jumpstarting the sluggish circadian rhythms, putting them back into the normal phase as they should be in the summer,” says Rohan.

The brightness of the light used for therapy is important. Most clinical trials investigating lightbox therapy use devices that can produce light at 10,000 lux (lux is the standard measurement for illumination). “Ten thousand lux is the intensity of the light that comes from the sky at sunrise on a clear day,” Rohan explains. (In contrast, “high noon on a clear day, you can get 100,000 lux. The average office is 500 lux.”)

It’s also key to maintain consistency when doing light therapy. “You need to do it regularly, consistently,” Rosenthal says. Rohan adds: “You have to stick with it, every day in the fall and the winter, and then do it again next year.”

Another treatment option is cognitive behavior therapy. Rohan has done research in which she asked people with SAD to identify the negative thoughts they have when they’re feeling depressed, and then question the accuracy of those thoughts.

“You can teach people to be aware of those [negative thoughts], and then question them, and reframe them, even if it’s just saying, ‘Okay, I prefer summer to winter,’” she says.

“How a shift in circadian rhythms can lead to the range of depressive symptoms characteristic of SAD is still not entirely clear.”

The next step is getting the person to become more proactive in how they cope with winter. Instead of hibernating, sleeping, and avoiding social engagements, they should be more active, pursuing hobbies and meeting with friends—“generally anything that’s fun and enjoyable that gets the person out of SAD and hibernation mode,” Rohan says.

Rohan’s own research has found evidence that people who suffer from SAD and who undergo cognitive behavior therapy experience fewer relapses and less severe symptoms over time than those treated with light therapy.

A study appearing in the Proceedings of the National Academy of Sciences in 2006 suggests that supplementary melatonin at low doses might be another way to treat SAD (although you should consult your healthcare professional to see if this method is right for you). This treatment option follows the theory discussed earlier—that SAD stems from “a mismatch between your circadian rhythms and your sleep/wake cycle [the cycle dictated by your alarm clock], and you need to realign them,” says Alfred Lewy, a professor emeritus of psychiatry at Oregon Health & Science University, who led the study. Earlier research by Lewy and others has shown that low doses of melatonin shift the body’s circadian rhythms.

For most people using melatonin to treat SAD, taking the supplement in the late afternoon is probably most effective, says Lewy. That’s because the supplemental dose will signal the body into thinking that dusk has fallen early, and levels of that dose will decline at around the time your body’s natural melatonin increase occurs.

Lewy recommends taking around 0.5 milligrams of melatonin, which is just above what the body naturally produces at night, but about 1/10 the normal dose sold in stores. (Lewy adds that people who are particularly susceptible to the sleep-inducing effects of melatonin—even at low doses—shouldn’t drive after taking the supplement.)

Some SAD sufferers who use light therapy in the morning might also benefit from low doses of melatonin in the late afternoon; Lewy says these treatments seem to be additive—the more of one you use, the less of the other you need.

Just like other forms of depression, though, if you’re experiencing symptoms of SAD, it’s important to consult a doctor rather than trying to self-diagnose and treat the problem.